Precision infrared (IR) optical devices such as waveplates, achromatic waveplate sets, modulators, Faraday rotators, compensators, and prisms are generally fabricated from semiconductor crystalline materials (one type of optical material) and used with lasers. These optical devices frequently suffer from the inability to handle high-average power applications due large variations in bulk power handling and ultimately optical device failure from laser damage. This variation in power handling is often caused by the fluctuating bulk resistivity of the semiconductor crystal, stemming from environmental exposure to shorter wavelength non-pass band light that includes photons of sufficient energy to promote electrons from the valence band to the conduction band or other mid-bandgap states of the semiconductor crystal. The promotion of electrons to these excited states often causes an increase in the free charge carrier density (electrons and holes) within the semiconductor crystal, which results in greater infrared (IR) absorption of higher wavelength(s) pass band light. This increased IR absorption can lead to localized heating from exposure to the higher wavelength(s) of pass band light, ultimately sometimes leading to the catastrophic breakdown of the optical device in high average power applications.
Other optical devices fabricated from insulator (dielectric) optical materials often suffer from similar inabilities to handle high power applications due to absorption mechanisms including electron-avalanche-breakdown where a combination of photons of non-pass band light (both shorter and longer wavelengths than the pass band) with pass band light leads to a cascade of promoted electrons across the insulator band gap. This creation of charge carriers leads to the greater absorption of the high intensity pass band light and can ultimately lead to the catastrophic breakdown of the optical device. Likewise optical devices fabricated from electric conductor or semiconductor optical materials such as metal mirrors or heated germanium optics suffer from a similar inability to handle high power applications due to mechanisms including the direct absorption of free carriers from the photons of light interacting with the optic surface. The absorption of any light increases the surface temperature (pass band or non-pass band) and can ultimately lead to the destruction of the optical device.
Known approaches to mitigate this non-pass band light triggered carrier generation problem for optical devices including an optical material have generally been to reduce the average power to which the optical device is exposed or to minimize the device exposure to the non-pass band light. This can be achieved by lowering the average laser power, building a secondary enclosure to shadow a majority of the ambient light from reaching the surface of the optical material, or by simply requiring the operator or technician to use the optical system in a dark room with only the laser light present around the optical material.